As computers and other electronic devices become smaller and faster, the demands placed on semiconductor devices utilized therein increase geometrically. Ultra-large-scale integration (ULSI) is a technology that places at least 1 million circuit elements on a single semiconductor chip. In addition to the tremendous density issues that already exist, with the current movement toward size reduction, ULSI is becoming even more delicate, both in size and materials than ever before. As current technology moves beyond ULSI, several barriers emerge that may be insurmountable with current wafer and substrate materials.
One barrier arises due to the accumulation of heat that may not be effectively channeled out of the crystal lattice of Group IV semiconductors. Semiconductors tend to have thermal conductivities that are a fraction of copper metal. Hence, semiconductor devices are often cooled with copper heat spreaders. However, as the power requirements future generations of semiconductor devices increase, copper heat spreaders will become reservoirs for heat accumulation.
Another barrier arises due to the accumulation of charge carriers, i.e. electrons and holes, which are intrinsic to quantum fluctuation. Accumulation of the carriers creates noise, and tends to obscure electrical signals within the semiconductor device. This problem is compounded as the temperature of the device increases. Much of the carrier accumulation may be due to the intrinsically low bonding energy and the directional anisotropy of typical semiconductor crystal lattices.
Yet another barrier may be a further result of current semiconductor materials. These materials tend to have a high leaking current and a low break down voltage. As the size of semiconductor transistors and other circuit elements decrease, coupled with the growing need to increase power and frequency, current leak and break down voltage also become critical.
As power and frequency requirements increase and the size of semiconductor components decreases, the search for materials to alleviate these problems becomes crucial to the progress of the semiconductor industry. One material that may be suitable for the next generation of semiconductor devices is diamond. The physical properties of diamond, such as its high thermal conductivity, low intrinsic carrier concentration, and high band gap make it a desirable material for use in many high-powered electronic devices.
The semiconductor industry has also recently expanded efforts in producing silicon-on-insulator (SOI) devices. These devices allow for electrical insulation between an underlying substrate and any number of useful semiconductor devices. Typically, these SOI devices utilize insulating layers with poor thermal conductivity, a high degree of thermal expansion mismatch, and/or difficulties in the epitaxial growth of silicon or other semiconductor materials.